The present invention relates to the acquisition of images representing ranges. Herein a range image is to be understood as a depiction of an object whose image points do not represent brightness values of emission or reflection and/or color of an individual point of the object, but the brightness represents the distance of the particular object point for example from the plane of the camera.
Methods are known for the two dimensional measurement and acquisition of range information i.e. distance information in the form of a range image as defined above; see for example P. Levi, Electronik 12, 1983. Generally speaking the known methods for acquiring range images can be divided into two groups which differ as to the physical measuring principle involved. In accordance with one method one determines range in terms of round trip travel time of electromagnetic or acoustic waves. In accordance with the other methods triangulation is involved. The first mentioned principle i.e. measuring travel time is suitable for distances larger than about 1 m up to infinity and, depending on the method involved, an accuracy of not less than 1 mm is attainable. The triangulation method is used primarily in the close up range i.e. under 1 m distance primarily for reasons of relationship between the measuring base line and the accuracy involved in triangulation.
The known methods as far as travel time measurements are concerned are disadvantaged by the fact that generally speaking one measures the distance between a particular point and a sensor. An image is now produced by means of a beam deviation for example under utilization of a rotating or oscillating mirror. In this case one acquires basically on a scanning basis measure point distance after the one. Such a system is basically mechanical and is quite expensive as far as optics is concerned.
Systems operating on the basis of triangulation permit under certain conditions that several object points are measured simultaneously if more than one line is envisageol. The system is disadvantaged by the fact that the acquired information is not unambiguous which means that the image evaluation becomes expensive. Moreover the method is clearly limited to the close up range.